The present invention relates to limiting damage caused by moisture, oxygen and other like oxygenated contaminants to OLED (organic light emitting diodes), organic transistors, flat panel displays, and other like electronic devices.
It is known that performance of electronic devices can be impaired by contact with moisture, oxygen and other oxygenated species. For example, semiconductor devices are undesirably oxidized by water and oxygen, and thereby degraded during contact with the same. The damage to these devices can be caused by as little as trace levels of these contaminants, thereby exacerbating this problem.
OLEDs are optoelectronic devices based on small molecules or polymers that emit light when an electrical current flows through the device. The devices are commercialized in the area of displays, screens, and signs. In addition, several products are commercially available in the area of cell phones, stereo displays, monitors, and military applications. In general, these devices incorporate Indium-Tin-Oxide (ITO) films, a conductive transparent film, as the anode, and a thin film of elements like Ba, Ca, Mg, Al, and the like, as the cathode. Sandwiched in-between the electrodes are carbon based films. The organic films consist of a hole injection layer, a hole transport layer, an emissive layer, and an electron transport layer. Polymer layers are used to transport the electrons and holes that are injected into another polymer film such as a polyphenylenevinylene or a “small molecule” organic film such as rubrene or Tris(hydroxyquinolato) aluminum. Light of any color can be generated by the polymer film or “small molecule” by selecting different polymers, dopants for the polymers, or different small molecules.
One recurrent problem of conventional OLED's is their apparent limited lifetime. The ‘brightness’ of the device decreases over the course of several months as a result of pixel shrinkage causing the quality of the product to diminish and eventually become non-useable. Generally, pixel shrinkage within the OLED is associated with moisture and other like contamination, where moisture permeating through encapsulating materials and sealants interacts with pixel materials, i.e., moisture degrades the OLED by degrading the hole transport material or causing the cathode material to delaminate and degrade. Moisture may also directly attack the light emitting molecules.
To overcome this problem in the industry, desiccants have been included in one form or another within OLEDs. For example, solids such as alkaline metal oxides, alkaline earth metal oxides, sulfates, metal halides, alkali metals, alkaline earth metals, aluminum carbide, aluminum-magnesium alloy, barium nitride alloy, and perchlorate-based desiccant materials have been used to protect OLEDs from damage caused by moisture. In some cases these desiccants are blended with binders to remove moisture from environment surrounding the OLED. However, these solid materials generally have low surface area, and not enough capacity, to capture the water continuously permeating from the outside environment into the interior of the OLED. Additionally, these solid materials do not have the capability to remove oxygen that permeates into the device and thereby causes performance degradation.
An alternative approach to removing moisture from an OLED environment is to use a lithium metal and magnesium metal deposits. However, the deposited lithium and magnesium materials do not have high surface areas to capture impurities, i.e., have low capacity.
Finally, the use of silica and zeolite that generally have high surface area have also been used to remove moisture from OLED's. However, the nature of these materials to capture the moisture via physical adsorption does not provide enough efficiency to protect the OLED for long periods of time. Also, these materials tend to emit moisture depending on the temperature condition of the device environment, where the materials are being employed due to the adsorption equilibrium.
In addition, some of the aforementioned desiccant materials do not have any capability, or very low capacity, for removing oxygenated species other than water. Therefore, damage to these devices caused by other oxygenated species are not minimized by the above described desiccants.
In all such cases regarding the removal of moisture from an OLED, there continues to be a need in the art for more effective removal techniques of moisture, and other oxygenated species, from the environment of a device.
In addition, there is a need in the art to have a signal or indication as to allow the user to determine if and when a device is in jeopardy of being damaged by moisture and other contaminants. In such case, a user may be alerted to the impending reduction in device quality due to moisture damage, and not spend additional time or money attempting to diagnose these problems. Against this backdrop the present invention has been developed.